Full color display based on organic light-emitting device

ABSTRACT

The conventional light-emitting element formed by an electroluminescent material has a problem due to poor color purity of light emission. Accordingly, it is an object of the present invention to provide a high luminance and high efficiency light-emitting device formed by an organic compound material. The invention provides a light-emitting device in which an organic compound layer that emits light having an emission peak with a half-band width of at most 10 nm upon applying current is interposed between a pair of electrodes is provided. The variation of emission peak intensity depending on a current density can be sorted by two linear regions with different gradients. A region of a sharp gradient is at a higher current density side compared to a region of a slow gradient. TFTs are provided to each pixel in order to perform active matrix driving.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a light-emitting device including an organiccompound material as a light emitting medium used for displaying images,a lighting, and the like.

2. Related Art

As a light-emitting device available in full color image display byarranging a plurality of light-emitting pixels in a matrix configuration(rows and columns), a light-emitting device available in full colordisplay by combining electroluminescent (EL) elements, each of whichemits light in different emission color (typically, red (R), green (G),and blue (B)) per pixel is well known. However, there has been a problemthat emission lifetime varies by emission color. Further, there has beena problem that a precision technique for patterning is required.

As another method, a method of combining a blue light-emitting elementand a color conversion layer can be nominated. There has been also aproblem that high practical color conversion efficiency cannot beobtained according to this method. In addition, it has been problematicthat a high efficiency blue light-emitting element has been required.

There is also a method that a white light-emitting element and a colorfilter are combined; however, there has been a problem that theusability of light emission is deteriorated, and so a high luminancewhite light-emitting element is required.

SUMMARY OF THE INVENTION

The problem in the above mentioned conventional techniques is caused bypoor color purity of light emission of a light-emitting element formedby an electroluminescent material. In view of the foregoing, it is anobject of the present invention to provide a high luminance and highefficiency light-emitting device formed by organic compound materials.

The present invention is to provide a light-emitting device having afeature that an organic compound material is used as a light emittingmedium, and coherent light and non coherent light from the organiccompound material, in other words, luminescence and laser light arecoupled out simultaneously or respectively. According to the invention,a material that produces electroluminescence is used. In order to emitlaser light in addition to the electroluminescence, a plurality ofdifferent organic compound materials is used to be stacked inconsideration of the wavelength. The thickness of each layer and thelamination configuration are determined for different purposes.

As used in the following, the term “organic compound layer” is a genericterm used to refer to a thin film containing mainly organic compoundsinterposed between a pair of electrodes. An organic compound layer isformed to be interposed between a pair of electrodes. An organiccompound layer is preferably formed by a plurality of layers, each ofwhich has different carrier transportation properties. Moreover, alight-emitting layer is included in the organic compound layer. Anorganic compound layer is preferably formed to have a resonatorstructure interposed between reflective layers.

In a light-emitting device according to the present invention, aplurality of layers are stacked as an organic compound layer so as toemit both coherent light and non coherent light by applying currentthrough the organic compound layer interposed between a pair ofelectrodes.

The light-emitting device is preferably formed to have a so-calledresonator structure, in which a reflector is provided to either or bothof surfaces of the organic compound layer inside the pair of electrodes.That is, a reflector is preferably provided to either or both ofsurfaces of the organic compound layer inside the pair of electrodes sothat a stationary wave is produced with respect to light at a specifiedwavelength emitted from the organic compound layer. Moreover, theorganic compound layer is preferably formed to have a thickness of ½time as a wavelength of laser oscillation (half wavelength) or integralmultiple of the same.

A light-emitting device used in the invention has a plurality ofemission peaks. In the light-emitting device, an organic compound layeremitting light having an emission peak with a half-band width of at most10 nm is interposed between a pair of electrodes.

Further, the light-emitting device is preferably formed to have aso-called resonator structure, in which a reflector is provided toeither or both of surfaces of the organic compound layer inside the pairof electrodes. That is, a reflector is preferably provided to either orboth of surfaces of the organic compound layer inside the pair ofelectrodes so that a stationary wave is produced with respect to lightat the wavelength determined by the film thickness. Moreover, theorganic compound layer is preferably formed to have a thickness of ½time of a wavelength of laser oscillation, that is, half wavelength, orintegral multiple of the same.

An organic compound layer used in the invention has the configurationcomposed of a hole injecting layer, a hole transporting layer, alight-emitting layer, an electron transporting layer, an electroninjecting layer, and the like. A material having hole transportationproperties such as hole mobility is referred to a hole injecting layeror a hole transporting layer. A material having electron transportationproperties such as electron mobility is referred to as an electroninjecting layer. Though the hole transporting layer and the holeinjecting layer are described respectively, they are the same in termsthat they have the common property of hole transportation as mostimportant property. As a matter of convenience, a layer adjacent to ananode is referred to as a hole injecting layer, and a layer adjacent toa light-emitting layer is referred to as a hole transporting layer.Further, a layer adjacent to a cathode is referred to as an electroninjecting layer, a layer adjacent to a light-emitting layer is referredto as an electron transporting layer. The light-emitting layer may serveas the electron transporting layer, and so it can be referred to as alight-emitting electron transporting layer. In addition, thelight-emitting layer may serve as a hole injecting layer, a holetransporting layer, an electron injecting layer, an electrontransporting layer, and the like. Further, the light-emitting layer canbe formed by metal complexes, organic dye materials, variousderivatives, or the like in order to vary emission color.

In a lamination configuration of such an organic compound layer,electrons injected from a cathode and holes injected from an anode arerecombined to form an exciton in the light-emitting layer, and theexciton radiates light while they are back to the ground state. Lightemission is obtained by so-called electroluminescence from the exciton.In a light-emitting device according to the invention, a holetransporting layer is formed on a light-emitting layer so as to emitlight having an emission peak with a half-band width of at most 10 nm ata central wavelength in a shorter wavelength side than a wavelength bandof the light that is generated in the light-emitting layer upon applyingcurrent. Thus, it is possible to induce laser light.

The invention is to provide a light-emitting device in which an organiccompound layer that emits light having an emission peak with a half-bandwidth of at most 10 nm upon applying current is interposed between apair of electrodes. The variation of emission peak intensity dependingon a current density can be sorted by two linear regions with differentgradients. A region of a sharp gradient is at a higher current densityside compared to a region of a slow gradient in the two linear regionswith different gradients.

The invention is to provide a light-emitting device in whichlight-emitting elements provided with the above mentioned organiccompound layer are arranged in a matrix configuration to form a pixelportion, and transistors for controlling light generated in thelight-emitting elements are connected to the light-emitting elements.

According to the invention, a high luminance and high efficiencylight-emitting device can be provided that couples out coherent lightand non coherent light, in other words, luminescence and laser light inorder to utilize the out-coupled light.

These and other objects, features and advantages of the presentinvention will become more apparent upon reading of the followingdetailed description along with the accompanied drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view, and FIGS. 1B and 1C are longitudinalcross-sectional views for showing a structure of a light-emitting deviceaccording to Embodiment mode of the present invention;

FIG. 2 is an explanatory top view for showing a structure of alight-emitting device according to Embodiment mode of the invention;

FIG. 3 is an explanatory cross-sectional view for showing a structure ofa light-emitting device according to Embodiment mode of the invention;

FIG. 4 is an explanatory cross-sectional view for showing a structure ofa light-emitting device according to Embodiment mode of the invention;

FIG. 5 is an explanatory cross-sectional view for showing a structure ofa light-emitting device according to Embodiment mode of the invention;

FIG. 6 is an explanatory cross-sectional view for showing a structure ofa light-emitting device according to Embodiment of the invention;

FIGS. 7A and 7B are graphs for showing a current density dependency,which is normalized by a maximum value of emission intensity, ofemission spectra of a light-emitting element manufactured according toEmbodiment;

FIG. 8 is a graph for showing an emission spectrum at current density of120 mA/cm² of a light-emitting element manufactured according toEmbodiment; and

FIGS. 9A to 9G are views for showing examples of electric appliancescompleted by using a light-emitting device according to the invention.

DESCRIPTION OF THE INVENTION

Embodiment Mode

Embodiment Mode of the invention is a light-emitting device in which anorganic compound layer having a plurality of emission peaks isinterposed between a pair of electrodes. One feature of thelight-emitting device is producing light emission having at least oneemission peak with a half-band width of at most 10 nm. An emission peakwith a narrow half band width can be realized by utilizing an organiccompound material and a lamination configuration as follows.

In an organic electroluminescent element, a large number of carriers aresupplied to an organic thin film. When applying current, the number ofcarriers presented in the element and the number of molecules presentedin the element becomes approximately the same, or the number of carriersbecomes larger than that of molecules. Therefore, the number ofmolecules with no carriers, that is, the number of molecules in a groundstate, is smaller than that of molecules with carriers. When anexcitation state is produced due to carrier recombination in this state,it becomes possible to create the state that the number of molecules inthe excitation state is relatively larger than that of molecules in aground state. Hence, it can be expected that population inversion can besufficiently produced by applying a small amount of current. When thethickness of an organic film serving as a resonator for the element isformed to be integral multiple of a half wavelength, it can be expectedthat laser oscillation can be realized by light amplification due toinduced radiation and resonation generated from the state of populationinversion.

FIG. 4 shows a structure of a top emission type light-emitting elementin which laser light is emitted from a top surface of a substrate. InFIG. 4, reference numeral 41 denotes a substrate, which is formed by anymaterials. For example, not only glass, quartz, plastic, but also aflexible substrate such as paper or cloth can be used. Of course, thesubstrate is not required to be transparent.

An anode 42 has a function of injecting holes to an organic compoundlayer. In addition, the anode 42 serves as a reflecting mirror.Therefore, a material that has poor absorption properties of visiblelight, high reflectivity, and large work functions (at least 4.0 eV) isrequired. As a material that meets the foregoing conditions, Ag, Pt, Au,or the like can be used. In addition, since the electrode is used as areflecting mirror, the electrode is required to have the thickness thatdoes not transmit visible light. Specifically, the electrode may beformed to have a thickness of from several ten nm to several hundredsnm.

An organic compound layer which emits light by applying current isformed over the anode 42. Specifically, a hole injecting layer 43, ahole transporting layer 44, a light-emitting layer 45, and an electrontransporting layer 46 and an electron injecting layer 47 are formed.

As the hole injecting layer 43, materials having small ionizationpotential, which are classified broadly into metal oxides, low molecularorganic compounds, and high molecular compounds are used. As examples ofthe metal oxides, vanadium oxides, molybdenum oxides, ruthenium oxides,aluminum oxides, and the like can be used. As examples of the lowmolecular organic compounds, starburst amine typified by m-MTDATA,metallophthalocyanine, and the like can be used. As examples of the highmolecular compounds, conjugated polymer such as polyaniline orpolythiophene derivatives can be nominated. By using the foregoingmaterials as a hole injecting layer, a hole injecting barrier is reducedto inject holes effectively.

As a typical example of the hole transporting layer 44, known materialssuch as aromatic amine can be preferably used. For example,4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (abbreviated α-NPD),4,4′,4″-tris(N,N-diphenyl-amino)-triphenyl amine (abbreviated TDATA), orthe like can be used. As high molecular materials, poly(vinyl carbazole)having excellent hole transportation properties can be used.

As the light-emitting layer 45, a metal complex such astris(8-quinolinolate) aluminum (abbreviated Alq₃),tris(4-methyl-8-quinolinolate) aluminum (abbreviated Almq₃),bis(10-hydroxybenzo[η]-quinolinato) beryllium (abbreviated BeBq₂),bis(2-methyl-8-quinolinolate)-(4-hydroxy-biphenylyl)-aluminum(abbreviated BAlq), bis [2-(2-hydroxyphenyl)-benzooxazolate] zinc(abbreviated Zn(BOX)₂), bis [2-(2-hydroxyphenyl)-benzothiazolate] zinc(abbreviated Zn(BTZ)₂), or the like can be used. Alternatively, varioustypes of fluorescent dye can be used. Further, phosphorescent materialssuch as a platinum octaethylporphyrin complex, atris(phenylpyridine)iridium complex, or atris(benzylidene-acetonato)phenanthrene europium complex can beefficiently used. Since phosphorescent materials have longer excitationlifetime than that of fluorescent materials, population inversion, thatis, the state in which the number of molecules in an excited state islarger that that in a ground state, becomes to be formed easily, whichis essential to laser oscillation.

In addition, light-emitting materials can be used as dopant in theforegoing light-emitting layer. Therefore, a material having largerionization potential and band gap than those of the light-emittingmaterial can be used as a host material, and a small amount of theforegoing light-emitting material (approximately from 0.001 to 30%) canbe mixed into the host material.

As the electron transporting layer 46, a metal complex having aquinoline skeleton or a benzoquinoline skeleton, or a mixed ligandcomplex thereof typified by tris(8-quinolinolate)aluminum (abbreviatedAlq₃) is preferably used. Alternatively, an oxadiazole derivative suchas 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviatedPBD), or 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazole-2-yl]benzene(abbreviated OXD-7), a triazole derivative such as3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviated TAZ), or3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviated p-EtTAZ), phenanthroline derivatives such asbathophenanthroline (abbreviated BPhen), or bathocuproin (abbreviatedBCP) can be used.

As the electron injecting layer 47, an alkali metal or alkaline earthmetal salt such as calcium fluoride, lithium fluoride, or cesium bromidecan be used. The cathode 48 is formed thereover. The cathode 48 may beformed by a metal having small work functions, an alloy, an electricalconductive compound, and mixture of the foregoing materials, each ofwhich is used for the general organic electroluminescent elements. Asspecific examples of the cathode material, an element of group 1 or 2 inthe periodic table, that is, an alkali metal such as Li, Cs, or thelike; alkali earth metal such as Mg, Ca, Sr, or the like; an alloycontaining the foregoing materials (Mg/Ag, Al/Li); or a transition metalcontaining a rare earth metal can be used. Alternatively, the cathode 48can be formed by stacking a metal such as Al, Ag, or ITO (includingalloys) with the foregoing materials. In addition, a resonator structureis required between the anode and the reflector over the cathode inorder to resonate light emission obtained from a light-emitting layer inthis embodiment mode. Therefore, as a cathode material, a metal havingpoor absorption of visible light and high reflectance is preferablyused. Specifically, Al, Mg, or an alloy of Al or Mg is preferably used.

The foregoing organic materials can be applied with either wet or dryprocess. In case of using high molecular materials, spin coating, inkjetting, dip coating, printing, or the like can be appropriately used.On the other hand, in case of using low molecular materials, not onlydip coating or spin coating, but also vapor deposition can be used. Theanode material and the cathode material may be applied with vapordeposition, sputtering, or the like.

The most important thing is an interval between the cathode and thereflecting mirror over the anode. The interval is required to beintegral multiple of a half wavelength for forming a stationary wave toamplify light. For example, in order to amplify light at 400 nm, aninterval at least 200 nm is required. Similarly, in order to amplifylight at 800 nm, an interval of 400 nm is required. The emissionwavelength of the foregoing organic light-emitting materials is mainlyin a visible light region. Therefore, in order to amplify the visiblelight defined as from 400 to 800 nm, the interval between the reflectormirror and the cathode 48, that is, the thickness of a functional layeris required to have a thickness of at least 200 nm. In addition, sinceit should consider that light speed is less for the refraction index ofa material, it is required that the value obtained by multiplying thethickness by refraction index is at least 200 nm.

The cathode 48 is formed to have transmittance of from 50 to 95% for thewavelength of laser oscillation. The cathode 48 may be formed to have athickness of from 5 to 20 nm in case of being formed by MgAg alloys.Alternatively, MgAg alloys having excellent electron injectionproperties can be stacked directly instead of forming the electroninjecting layer 47. In this instance, since laser light is emitted froma top surface, the cathode 48 serves as an output mirror. Accordingly,the cathode is formed to have transmittance of from 50 to 95% for thewavelength of laser oscillation. For example, an MgAg alloy is formed tohave a thickness of from 5 to 20 nm.

FIG. 5 shows the state that a reflecting mirror is located over theunderside of a transparent electrode. Therefore, the thickness of anorganic compound layer can be reduced and laser light can be oscillatedfrom the top surface of a substrate by the structure in which thetransparent electrode is incorporated into a part of a resonator.

In FIG. 5, a substrate 51 can be formed by any materials. For example,not only glass, quartz, plastic, but also a flexible substrate such aspaper or cloth can be used. Of course, the substrate is not required tobe transparent. A reflecting mirror 52 is provided over the substrate51. As the reflecting mirror 52, a material that has high reflectivityand poor absorption properties for visible light is selected.Specifically, metals such as Al, Ag, or the like; alloys containingmainly the foregoing metals; or a laminated film of derivatives such asSiO₂, TiO₂, or the like can be used. In a derivative laminated film, thethickness of each layer is determined so as to reflect selectively lightwith an oscillation wavelength. The derivative laminated film is formedby stacking some layers required for total reflection. An electrode 53is formed over the reflecting mirror 52. The electrode 53 is required toinject holes to an organic compound layer and have high transparency.For the electrode 53, a transparent electrode such as ITO, TiN, or thelike is preferably used.

Over the electrode 53, the same structure as that of an organicelectroluminescent element that emits light upon applying current. Thatis, a hole injecting layer 54, a hole transporting layer 55, alight-emitting layer 56, and an electron transporting layer 57 areformed. These layers may be formed by the foregoing materials. In thehole injecting layer 54, the hole transporting layer 55 and the electrontransporting layer 57, a layer that does not contribute light emissionis not necessarily formed. The electron injecting layer 58 is generallyformed over the electron transporting layer 57. An organic compounddoped with an alkali metal such as Li, Ce, or the like is preferablyused. Thereafter, a cathode 59 is formed. The cathode 59 may be formedby the foregoing materials. Alternatively, MgAg alloys having excellentelectron injection properties can be stacked directly instead of formingthe electron injecting layer 58. In this instance, since laser light isemitted from a top surface, the cathode 59 serves as an output mirror.Accordingly, the cathode is formed to have transmittance of from 50 to95% for the wavelength of laser oscillation. For example, an MgAg alloyis formed to have a thickness of from 5 to 20 nm.

By applying current to thus formed light-emitting element, a part oflight amplified from the organic compound layer resonates between thecathode and the anode, and a stationary wave is formed. Here, theresonator is formed to have a thickness including the thickness of thetransparent electrode. Accordingly, the thickness of the organiccompound layer can be reduced. Hence, light can be emitted at lowvoltage. Accordingly, laser can be oscillated at low voltage andelectroluminescence can be emitted simultaneously.

A light-emitting device using the above described light-emitting elementis explained with reference to FIGS. 1 and 2. A light-emitting deviceaccording to this embodiment mode uses the above describedlight-emitting element to create a display by using non coherent laserlight and coherent laser light due to fluorescence and phosphorescenceupon applying an electric field. FIG. 1A is a perspective view forshowing the structure of the light-emitting device without an externalcircuit or the like. FIG. 1B is a cross-sectional view of FIG. 1A takenalong the line A-A′. FIG. 1C is a cross-sectional view of FIG. 1A takenalong the line B-B′.

The light-emitting device has a element substrate 10 installed with animage display portion 12, a scanning line drive circuit 13, a data linedrive circuit 14, an input terminal unit 15, and the like. The elementsubstrate 10 is fixed to an opposing substrate 11 provided with a colorfilter 18 by sealing agent 19.

As the element substrate 10, glass, quartz, plastic, semiconductor, orthe like is used. As the opposing substrate 11, glass, quartz, plastic,or the like transmitting at least visible light is used as a member. Thesubstrate can be formed into any shape such as a plate, a film, or asheet in a single layer structure or a laminated layer structure. Asglass, a transparent glass such as a commercially available non-alkaliglass is preferably used. As a glass substrate, an alkali glass coatedwith a silicon oxide film can be used. In case of using plastic,polyethylenenaphthalate (PEN), polyethylene terephthalate (PET),polyether sulfone (PES), transparent polyimide, or the like can be used.In addition, transparent ceramic such as transparent alumina or ZnSsintered body can be used.

The sealing agent 19 is formed along with the edge of the opposingsubstrate 11. The sealing agent 19 is formed to overlap with thescanning line drive circuit 13 and the data line drive circuit 14 via aninterlayer insulating film 16. The interlayer insulating film 16 isformed with a flatness surface, and a top surface and a side portion ofthe interlayer insulating film 16 are formed by silicon nitride orsilicon oxynitride. In the image display portion 12, a matrix is formedwith data lines and scanning lines extended from the scanning line drivecircuit 13 or the data line drive circuit 14. A pixel matrix is composedof a crop of switching elements located appropriately in various placesand a crop of light-emitting elements 17 connected electrically to thecrop of switching elements. The scanning line drive circuit 13 is drivenfrom both sides of the image display portion 12; however, the scanningline drive circuit 13 may be driven from only either side of the imagedisplay portion 12 in case that the problem of signal delay isvanishingly small.

Color filters 18 corresponding to the crop of light-emitting elements 17capable of displaying multicolor are provided. The color filters 18 areappropriately composed of a filter for transmitting a specifiedwavelength corresponding to each pixel, a sharp cut filter for cutting awavelength of at most limited transmittance, and a color correctionfilter. Alternatively, a color conversion layer can be used with theforegoing filters.

Here, the crop of light-emitting elements 17 is composed oflight-emitting elements emitting specific light having at least oneemission peak with a half-band width of at most 10 nm. In this instance,a band path filter for specified light and a filter transmitting aspecific wavelength as the color filters 18 are located corresponding toeach pixel.

The input terminal unit 15 is formed at the periphery of the elementsubstrate 10. The input terminal unit 15 receives various signals froman external circuit and connects to a power source. Space surrounded bythe element substrate 10, the opposing substrate 11, and the sealingagent 19 is filled with an inert gas. By filling the inert gas, the cropof light-emitting elements 17 is protected from corrosion. Drying agentsuch as barium oxide may be provided in the space.

FIG. 2 is a top view of the element substrate 10 for showing thestructure thereof in detail. The structure of the element substrate 10shows the arrangement of the scanning line drive circuit 13 enclosingthe two sides of the image display portion 12 and the data line drivecircuit 14 adjacent to other side of the image display portion 12 andthe input terminal unit 15.

In FIG. 2, compartmentalized one pixel region 23 is arranged in rows andin columns to compose the image display portion 12. A first auxiliarywiring 20 is formed in stripe parallel to columns. The both ends or theeither end of the first auxiliary wiring 20 is extended to outside ofthe image pixel portion. The first auxiliary wiring 20 is formed toprevent from overlapping with the one pixel region 23 so as not tointerfere with an opening ratio. A second auxiliary wiring 21 connectedelectrically to the first auxiliary wiring 20 is extended in parallel torows. The both ends or either end of the second auxiliary wiring 21connects electrically to a wiring 22 extended from the input terminalunit 15. Constant potential or alternation potential may be applied tothe wiring 22 depending on the drive method of the organicelectroluminescent element.

The auxiliary wiring is preferably formed by a material havingresistivity of at most 1×10⁻⁵ Ωcm. The value of resistance of theauxiliary wiring per 1 cm is preferably at most 100Ω. Needless to say,the value of resistance of the auxiliary wiring is determined by a linewidth and a thickness besides a material to be formed. For, example, incase that the pitch between pixel rows is 200 μm, the first auxiliarywiring formed over a bank layer is appropriately formed to have a widthof from 20 to 40 μm given that the width of the pixel electrode isapproximately 120 μm. In case that the auxiliary wiring is formed byaluminum alloys having resistivity of 4×10⁻⁶ Ωcm to have a thickness of0.4 μm, the value of resistance becomes 50Ω per 1 cm when the line widthis 20 μm.

FIG. 3 is a cross-sectional view showing the structure of alight-emitting device. A pixel (A), a pixel (B), and a pixel (C) areformed over the element substrate 10. A light-emitting element 251connected to a thin film transistor (hereinafter, TFT) 201 is providedto the pixel (A). A light-emitting element 252 connected to a TFT 202 isprovided to the pixel (B). A light-emitting element 253 connected to aTFT 203 is provided to the pixel (C). The TFTs and the light-emittingelements are formed via an interlayer insulating film 204.

Each electrodes 205 a to 205 c is formed over the interlayer insulatingfilm 204 to connect electrically to the TFT of each pixel.

The light-emitting element is formed to sandwich an organic compoundlayer between the electrode 205 a and other electrode 210. The structureof the organic compound layer can be varied depending on the emissioncolor of each pixel. Other than a light-emitting layer, that is, a holeinjecting layer, a hole transporting layer, an electron injecting layer,and an electron transporting layer, may be shared by each pixel.

In FIG. 3, a hole transporting layer 206 and an electron transportinglayer 209 are formed by one layer to be shared by each pixel. Alight-emitting layer 207 is shared by the pixels (A), (B). Alight-emitting layer 208 formed by another material is provided to thepixel (C).

As in the present invention, in case that a light-emitting element thatemits light having a plurality of emission peaks and having an emissionspectrum distributed throughout a specified wavelength band is used,light can be coupled out selectively by a coloring layer of a colorfilter 18 provided corresponding to the pixel. A pixel that can coupleout coherent light by locating a coloring layer serving as a band pathfilter can be provided to a light-emitting element capable of emittingnon coherent light (electroluminescence) and coherent light (laserlight). Therefore, a pixel portion that can display an image by couplingout respectively non coherent light (electroluminescence) and coherentlight (laser light) using an optical filter can be provided.

The space between the opposing substrate 11 and the element substrate 10may be filled with light-transmitting resin or a dried inert gas, ordepressurized in order to seal the light-emitting element.

In this embodiment mode, a transistor provided to a pixel is formed by aTFT; however, the invention is not limited thereto. A TFT composed of aMOS transistor formed over a single crystalline semiconductor substrateor a SOI (Silicon On Insulator), or an amorphous semiconductor film suchas silicon can be formed.

Embodiment

Hereinafter, an example of a light-emitting element capable of beingapplied for the present invention will be explained with reference toFIG. 6.

As a substrate for forming a film such as an electrode or alight-emitting layer, a glass substrate 101 such as commerciallyavailable alumino silicate glass, barium borosilicate glass, and thelike are preferably used. Over the glass substrate, an ITO film isformed by sputtering to have a thickness of from 30 to 100 nm as thefirst electrode (anode) 102.

As the hole transporting layer 103,4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]-biphenyl (NPB) is deposited byvacuum vapor deposition to have a thickness of 135 nm. As thelight-emitting layer 104, 4,4′-bis(N-carbazolyl)-biphenyl (CBP) as ahost material and an iridium complex, Ir(tpy)₂(acac) as a tripletlight-emitting material are deposited to have a thickness of 30 nm byco-evaporation. The weight ratio of the CBP and the iridium complex is10:1. The electron transporting layer 105 is formed thereover bybathocuproin (BCP) to have a thickness of 105 nm. The electron injectinglayer 106 is formed by calcium fluoride (CaF₂). The second electrode 107is formed by Al (aluminum) by vapor deposition.

The film thickness of each layer formed by organic materials isdetermined so as to amplify light generated in an organic compoundlayer. Therefore, the light emission from the Ir complex, which is addedto the light-emitting layer 104, or the light emission from the holetransporting layer 103 preferably form a stationary wave by repeatingreflection at the interface between the first electrode 102 and the holetransporting layer 103, the interface between the electron transportinglayer 105 and the electron injecting layer 106, or the interface betweenthe electron injecting layer 106 and the second electrode 107.

Materials capable of emitting light are the Ir complex and the NPB inthe organic compound materials used here. These materials give lightemission in a visible light region (400 to 800 nm). In order to form astationary wave, the intervals between reflective surfaces are requiredto be the integral multiple of a half wavelength. For example, in orderto form a stationary wave of 400 nm, the intervals are required to be200 nm or the integral multiple thereof. That is, the thicknesses arerequired to be integral multiple of 200 nm, such as 200, 400, or 600 nm.Similarly, in order to form a stationary wave of light at 800 nm, theintervals between the reflective surfaces, that is, the thicknesses arerequired to be integral multiple of 400 nm, such as 400, 800, or 1200nm.

By way of embodiment, the hole transporting layer 103 is formed to havea thickness of 135 nm, the light-emitting layer 104 is formed to have athickness of 30 nm, and the electron transporting layer 105 is formed tohave a thickness of 105 nm. As a result, the organic compound layer isformed to have a thickness of 270 nm in total. In this case, given thatthe refractive index of organic compound layer is 1.7, the wavelength oflight capable of forming a stationary wave is the one that is divided920 nm by integer, that is, 460 nm in a visible light region.

FIGS. 7A and 7B show an emission spectrum of a thus obtainedlight-emitting element. Light emission is obtained by applying directvoltage to a pair of electrodes with the first electrode serving as ananode and the second electrode serving as a cathode. Light emission canbe observed at an applied voltage of around 6 V. Light emission of tensof thousands candela (Cd) is obtained at an applied voltage of 24 V.

In both spectra shown in FIGS. 7A and 7B, normalized emission intensityis shown. FIG. 7A shows an emission spectrum of a face emission observedfrom the side of the first electrode. FIG. 7B shows an emission spectrumof an edge emission observed from a lateral side of the substrateprovided with a laminated organic compound layer. As shown in FIG. 7A,intense emission is observed in a wavelength band of from 475 to 650 nm.The emission is produced from the Ir complex. Another emission isobserved at around 400 to 475 nm. The emission is produced from the NPB.

The measurement shows that carriers (holes and electrons) are recombinedeach other almost always in the light-emitting layer 104 to excite thelight emission from the Ir complex; however, some carriers arerecombined in the hole transporting layer 103. In case of the faceemission, emission intensity varies depending on the variation of acurrent density. Therefore, the spectra at any current density become tohave identical forms, and only the intensity is increased linearly inproportion to the increase of a current density.

Compared to the spectrum shown in FIG. 7A, the spectrum of the edgeemission has two features. The first feature is that the waveform of anemission spectrum in the wavelength band of from 475 to 650 nm isdifferent from that in FIG. 7A. The second feature is that a sharpemission spectrum is observed around 460 nm in FIG. 7B. The reason ofthe former is not clear. On the contrary, the reason of the latter maybe considered that a stationary wave is formed by the organic compoundlayer 102, and only the light emission at the wavelength is amplified.Actually, as mentioned above, the wavelength which allows stationarywave is 460 nm in the organic compound layer 102 with the thickness. Asthe most characteristic feature, the intensity of the emission in thewavelength band of from 475 to 600 nm varies in proportion to theincrease of a current density, on the contrary, the intensity of anotheremission spectrum having a peak at around 460 nm further increases thanthe increase of a current density. Therefore, in the normalizedintensity shown in FIG. 7B, only emission at 460 nm is relativelyincreased.

Therefore, the measurement shows that the structure of thelight-emitting device serves as a resonator of light at 460 nm toamplify the light. FIG. 8 shows a result of increasing a currentdensity. As shown in FIG. 8, a spectrum shape of face emission is notvaried at all at a current density of 120 mA/cm². On the contrary, theintensity of edge emission is increased at 460 nm; therefore sharpemission intensity is obtained.

Table 1 shows laser oscillation characteristics of a sample manufacturedaccording to Embodiment. Table 1 is the measurement result of the samplein three pieces showing a peak wavelength of from 462 to 464 nm, ahalf-band width of at most 10 nm, and a threshold of from 10 to 12.5mA/cm² and presenting a good repeatability. These characteristics aremeasured at room temperature.

TABLE 1 threshold peak wavelength half-band width^([1]) sample No.(mA/cm²) (nm) (nm) 1 12.5 464 8.0 2 10.0 462  8.0^([2]) 3 11.0 463 9.1^([1])half-band width of 50 mA/cm², ^([2])half-band width of 60 mA/cm²

Accordingly, the light-emitting device has a resonator structure forlight emission around 460 nm to form a stationary wave of light at thewavelength. Further, light emission of 460 nm denotes threshold to acurrent density. The behavior is similar to that of a solid laser. Incase that the threshold indicates that what is called populationinversion is started, laser light is oscillated at a further largecurrent density.

The invention can be practiced by utilizing another lamination structureformed by another material, in case that the invention is not limited tothe foregoing structure of the light-emitting element, and thatelectroluminescence and laser light can be coupled out simultaneously orrespectively.

In a light-emitting device according to the invention shown in FIG. 3,the case that a light-emitting element according to this embodiment willbe explained. A light-emitting layer 207 is shared by a light-emittingelements 251, 252 to use an organic compound layer according to thisembodiment. When a coloring layer 211 is formed by a blue filtercorresponding to the light-emitting element 251, laser light having anemission peak at 460 nm. A coloring layer 212 is formed by a greenfilter for the light-emitting element 252. In a light-emitting element253, a light-emitting layer 208 is formed into a red light-emittinglayer by using different materials and by doping red emission dye intoAlq₃ or TPD. The color purity of emission color of the light-emittingelement 253 can be improved by using a red color filter as a coloringlayer 213. A blue filter may be used as a coloring layer 211 for thelight-emitting element 251. A blue cut filter may be used as a coloringlayer 212 for the light-emitting element 252.

Accordingly, a light-emitting device available in full color display(red (R), green (G), blue (B)) can be thus manufactured.

Various electric appliances can be completed by using the abovementioned light-emitting device according to the invention, such as apersonal digital assistant (an electronic book, a mobile computer, acellular phone, and the like), video camera, digital camera, computer, aliquid crystal TV set, cellular phone, and the like.

FIG. 9A illustrates an example of a TV set applied with the inventioncomposed of a housing 301, a support 302, a display portion 303, and thelike. The TV set can be completed by using a light-emitting deviceaccording to the invention as a display portion 303.

FIG. 9B illustrates an example of a video camera applied with theinvention composed of a main body 311, a display portion 312, a soundinput unit 313, operation switches 314, a battery 315, an imagereception portion 316, and the like. The video camera can be completedby using a light-emitting device according to the invention as a displayportion 312.

FIG. 9C illustrates an example of a computer applied with the inventioncomposed of a main body 321, a housing 322, a display portion 323, a keyboard 324, and the like. The computer can be completed by using alight-emitting device according to the invention as a display portion323.

FIG. 9D illustrates an example of a PDA (Personal Digital Assistant)applied with the invention composed of a main body 331, a stylus 332, adisplay portion 333, operation buttons 334, an external interface 335,and the like. The PDA can be completed by using a light-emitting deviceaccording to the invention as a display portion 333.

FIG. 9E illustrates an example of a sound reproduction device appliedwith the invention, in specific, an in-car audio system composed of amain body 341, a display portion 342, operation switches 343, 344, andthe like. The sound reproduction device can be completed by using alight-emitting device according to the invention as a display portion342.

FIG. 9F illustrates an example of a digital camera applied with theinvention composed of a main body 351, a display portion (A) 352, aneye-piece portion 353, operation switches 354, a display portion (B)355, a battery 356, and the like. The digital camera can be completed byusing a light-emitting device according to the invention as displayportions 352, 355.

FIG. 9G illustrates an example of a cellular phone applied with theinvention composed of a main body 361, a sound output portion 362, asound input portion 363, a display portion 364, operation switches 365,an antenna 366, and the like. The cellular phone can be completed byusing a light-emitting device according to the invention as the displayportion 364.

These electric appliances are illustrative only. A light-emitting deviceaccording to the invention is not limited thereto, but can be used as ameans for displaying images in a washing machine, a refrigerator, a landline, a game machine, a microwave oven, a radio, and the like.

Although the present invention has been fully described by way ofexamples with reference to the accompanying drawings, it is to beunderstood that various changes and modifications will be apparent tothose skilled in the art. Therefore, unless otherwise such changes andmodifications depart from the scope of the present invention hereinafterdescribed, they should be construed as being included therein.

1. A light-emitting device comprising: a first light emitting elementcomprising a first light emitting layer interposed between a first pairof electrodes; a second light emitting element comprising the firstlight emitting layer interposed between a second pair of electrodes; athird light emitting element comprising a second light emitting layerinterposed between a third pair of electrodes; and a first coloringlayer, a second coloring layer, and a third coloring layer provided overthe first light emitting element, the second light emitting element, andthe third light emitting element, respectively; wherein the second lightemitting element is adjacent to the first light emitting element and thethird light emitting element; wherein the first light emitting layerextends from the first light emitting element to the second lightemitting element and is shared by the first light emitting element andthe second light emitting element; wherein the first coloring layer, thesecond coloring layer, and the third coloring layer are different incolor from each other, wherein the first light emitting layer and thesecond light emitting layer are different in emission color from eachother, and wherein the second light emitting layer overlaps an edgeportion of the first light emitting layer.
 2. A light-emitting deviceaccording to claim 1, wherein the first light emitting element furthercomprises a hole transporting layer and an electron transporting layerwith the first light emitting layer therebetween, and wherein a totalthickness of the hole transporting layer, the first light-emitting layerand the electron transporting layer is arranged to be equal to anintegral multiple of a value that is obtained by dividing a wavelengthof an emission peak of the hole transporting layer by refraction indexof a layer consisting of the hole transporting layer, the first lightemitting layer, and the electron transporting layer.
 3. A light-emittingdevice according to claim 1, wherein the first light emitting element iscapable of emitting laser light.
 4. A light-emitting device according toclaim 1, wherein the third light emitting element further comprises ared emission dye.
 5. A light-emitting device according to claim 1,wherein the first light emitting element further comprises a reflectorunder one of the first pair of electrodes which is opposite to the firstcoloring layer.
 6. A light-emitting device according to claim 1, whereinthe first light emitting element further comprises a hole transportinglayer and an electron transporting layer with the first light emittinglayer therebetween, and wherein one of the first pair of electrodeswhich is closer to the first coloring layer has transmittance of from 50to 95% for the wavelength of emission from the hole transporting layer.7. The light-emitting device according to claim 1, wherein thelight-emitting device is used for a display portion of an electronicapparatus selected from the group consisting of TV set, video camera,computer, sound reproduction device, digital camera, and cellular phone.8. A light-emitting device comprising: a first thin film transistor, asecond thin film transistor and a third thin film transistor formed overa substrate; a first light emitting element which comprises a firstlight emitting layer interposed between a first pair of electrodes andis electrically connected to the first thin film transistor; a secondlight emitting element which comprises the first light emitting layerinterposed between a second pair of electrodes and is electricallyconnected to the second thin film transistor; a third light emittingelement which comprises a second light emitting layer interposed betweena third pair of electrodes and is electrically connected to the thirdthin film transistor; and a first coloring layer, a second coloringlayer, and a third coloring layer provided over the first light emittingelement, the second light emitting element, and the third light emittingelement, respectively; wherein the second light emitting element isadjacent to the first light emitting element and the third lightemitting element; wherein the first light emitting layer extends fromthe first light emitting element to the second light emitting elementand is shared by the first light emitting element and the second lightemitting element; wherein the first coloring layer, the second coloringlayer, and the third coloring layer are different in color from eachother, wherein the first light emitting layer and the second lightemitting layer are different in emission color from each other, andwherein the second light emitting layer overlaps an edge portion of thefirst light emitting layer.
 9. A light-emitting device according toclaim 8, wherein the first light emitting element further comprises ahole transporting layer and an electron transporting layer with thefirst light emitting layer therebetween, and wherein a total thicknessof the hole transporting layer, the first light-emitting layer and theelectron transporting layer is arranged to be equal to an integralmultiple of a value that is obtained by dividing a wavelength of anemission peak of the hole transporting layer by refraction index of alayer consisting of the hole transporting layer, the first lightemitting layer, and the electron transporting layer.
 10. Alight-emitting device according to claim 8, wherein the first lightemitting element is capable of emitting laser light.
 11. Alight-emitting device according to claim 8, wherein the third lightemitting element further comprises a red emission dye.
 12. Alight-emitting device according to claim 8, wherein the first lightemitting element further comprises a reflector under one of the firstpair of electrodes which is opposite to the first coloring layer.
 13. Alight-emitting device according to claim 8, wherein the first lightemitting element further comprises a hole transporting layer and anelectron transporting layer with the first light emitting layertherebetween, and wherein one of the first pair of electrodes which iscloser to the first coloring layer has transmittance of from 50 to 95%for the wavelength of emission from the hole transporting layer.
 14. Thelight-emitting device according to claim 8, wherein the light-emittingdevice is used for a display portion of an electronic apparatus selectedfrom the group consisting of TV set, video camera, computer, soundreproduction device, digital camera, and cellular phone.